Collisions in sha256 are possible, but at the moment only in 2^256 operations or 2^128 operations if you have enough memory for a birthday attack.I'm sure some day a faster way to find collisions will be found, just like happened with md5.But I'm also willing to bet another 10 BTC (I'm just not as rich as others) it won't happen this year.

I'll post the research paper once more, soon. 6K if it can be used to compute hashes faster, was it?

"Faster" as in "within reasonable time". Not as in: reducing the number of expected attempts from 2255 to 2243 or something, cause that's still way beyond reasonable and wouldn't make sha256 significantly less secure.

Allow me to throw in some numbers. If we were to use brute force only, without any trickery or sha256-specific attacks, there are 2256 possible hashes and by average we'd have to do 2256/2 = 2255 ≈5.8×1076 attempts to find a collision. When using, say, this $15,295 mining rig which does 25.2 GigaHash/s, it would take ±2.3×1066 seconds ≈7.3×1058 years. For your reference: the current age of the universe is estimated at a mere 1.37×1010 years

So, even if you could speed up the computation of hashes by a trillion times (which would be quite an impressive achievement) it would take you 5328467153284670278835433757793583104 times the age of the universe to find a hit.

Let's put it otherwise: can you post a single collision (two different pieces of data having the same sha256 hash) somewhere later this month? Good luck sir

Even better, is the practical application of finding a collision. That is, get the private key of a public key that has a lot of bitcoins in it. Then cash out. This will be advertised all over the media as a hack or a theft, and everyone will know about it.

Or, mine a block every 10 minutes (don't make it every minute or else people will get suspicious.) and keep the rewards. This will go unnoticed for a few days or a few weeks, depends on several other factors. So you can get BTC 5k every day or something like that.

Or, get the private keys of several public keys, do some salami slicing (get 0.01 BTC from every address). Then cash out. This will be broadcast all over the media eventually, after someone figures out what's happening, but it can take awhile, or people will not notice they just lost 0.01 BTC and not pay attention. This is feasible only if you have actually broken SHA256 and can get several targeted collisions on several bitcoin addresses.

Dabs: SHA-256 isn't used to sign transactions. You can't use it to steal money directly. You could exploit weaknesses by forking the blockchain, or, more practical, just earn a lot of BitCoins by mining at a not-too-suspicious rate. Even then, you need something better than just the ability to find a random collision.

5000 is a little to much I think, only 24*6*50 = 7200 / day are mined, so 5000 is almost 70% of total.If you just mine 5% it is 360 BTC, somewhere like $1800 a day, it is much harder to notice so the chance of someone finding out is much less likely.

If you break SHA the best thing to do would be to quietly let gavin know and wait for bitcoin to be fixed with an announcement that you broke it and were responsible for no one being ripped off because you only let gavin know, and the BTC "thankyou" payments will start rolling in